1. Field of the Invention
The present invention generally relates to a method for testing computer system, and more particularly, to a method for verifying clock signal frequency of a sound interface of the computer system.
2. Description of the Prior Art
The trend of multimedia appliance of computer industry brings forward wide use of sound interface in computers, especially personal computers. The computer sound interface is commonly made as a sound blaster card or audio card adapted to be plugged in an expansion slot of a computer. Typically, the computer sound card available in the markets is provided with at least one sound data output port into which an audio output device, such as a speaker, can be plugged. Some of the computer sound cards are further provided with a sound data input port for receiving external sound data from for example a microphone and then applying the received sound data to the computer.
Typically, a sound interface of a computer system comprises a number of components, including an analog-to-digital converter, an audio signal coding/decoding (CODEC) circuit, a digital signal processor, and a digital-to-analog converter. The audio signal that the sound interface receives from a microphone is in the analog form. Such an analog signal may be converted by the analog-to-digital converter into digital data. Since the digital sound data is usually huge, most of digital signal processors are capable to compress the digital sound data in order to save storage space. The compressed digital sound data is then transmitted to a central processing unit of the computer to be stored in a data storage device for example a hard disk in a predetermined data format, such as WAV format.
In replaying the sound data, the central processing unit of the computer first retrieves the compressed sound data from the hard disk or other data storage device, such as a compact optical disk (CD-ROM). The compressed sound data is then processed by the digital signal processor to decompress the digital sound data. The decompressed sound data is then processed by the digital-to-analog converter to generate a continuous analog signal which can then be applied to drive a sound output device, such as a speaker. Since the data of the sound data is typically very huge, most of the sound cards adapt DMA (Direct Memory Access) technique for transfer of the data of the sound data.
However, since the sound data is sampled at a frequency determined by a clock signal supplied by a clock signal generator, an incorrect clock signal frequency may lead to noises or abnormal sounds generated in the sound output device.
Conventionally, an oscilloscope can detect and determine if the clock signal frequency of the sound interface is correct. Such an operation is, however, very time-consuming and is thus not suitable for mass production requirements.